Electrical regulating system



July 10, 1951 R. R. LOBOSCO ELECTRICAL REGULATING SYSTEM Filed May 11, 1948 COMPENSATING CIRCUIT INVENTOR ROSCOE R.LOB.OSCO BY ATTORNEY Patented July 10, 1951 ELECTRICAL REGULATING SYSTEM Roscoe R. Lobosco, Elizabeth, H. J., assignor, by

mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York Application May 11, 1948, Serial No. 26,263

6 Claims. (Cl. 318-331) This invention relates to electrical regulating systems, and more particularly to electronic circuits adapted to control a variable characteristic which is adjustable.

The present application is a continuation-inpart of application Serial No. 550,731, filed August 23, 1944 (now Patent No. 2,445,789, dated July 27, 1948), which discloses a motor-speed governor circuit the principal features of which include an unusually wide adjustable motorspeed range of 100 to 1 or greater, very good speed-load regulation in comparison with other governors having a comparable range, and a relatively simple and inexpensive circuit. It is the purpose of the present invention to further improve the speed-load regulation, to further extend the useful speed range, and to provide a very simple and inexpensive circuit for limiting the motor starting current and yet obtain a wide speed range and good regulation.

When starting a motor, it is usually necessary to provide some means of limiting the starting current in order to protect both the motor and the power supply circuit. With D. C. motors, such as are usedwith the electronic governor of application Serial No. 550,731, the starting current is usually limited by inserting a resistor in series with the armature during the starting period. This resistor is automatically shorted out after the starting period, because it increases the motor speed-load regulation to a very large value if it is left in the circuit. The increase in regulation due to the inclusion of the starting resistor in the armature circuit is not as great with the electronic governor of application Serial No. 550,731 as it is with more conventional circuits, but it is nevertheless sometimes larger than desirable. For this reason, in the past means have been provided for shorting out the starting resistor used in such governor. Since the operation is automatic, this involves .a starting timer, a starting relay, complicated switch gear, and complicated circuits to recycle the starting operations. Some other past means have involved the use of relatively complicated and expensive circuits to accomplish the same purpose. Thus, such starting equipment represents an appreciable part of the cost of such governor.

The main object of this invention'is to provide a novel circuit which further improves the performance of the governor, simplifies the motor starting means, and lowers the cost of the governor.

The drawing is a simplified circuit diagram illustrating the invention as applied to the automatic speed-control of a shunt motor.

An alternating current supply circuit i is connected to a control circuit 2 by a master switch 3, and safety fuses 4 are provided in the power supply conductors of such control circuit 2. A pilot light 5 is connected across such conductors to indicate when the circuit 2 is energized. Connected to the circuit 2 are primary windings 6, I and 8 of transformers 9, l and H. The primary winding 8 is connected to the circuit 2 by a normally open switch I2 of a time delay relay [3 which is also connected across such circuit. Upon closing the switch 3, the time delay relay I3 is adapted to close the switch 12 after a suitable time interval, permitting the cathode heater H of a grid-controlled gaseous discharge tube or thyratron l to become hot. such heater being connected to the secondary winding l6 of transformer by conductors l'l.

Transformer H supplies the motor armature power through the gaseous tube l5. The anode I8 of the thyratron I5 is connected to ground at l9 through the secondary winding of the transformer II. The cathode 21 of thyratron I5 is connected by a conductor 22 to the armature winding 23 of a direct current shunt motor 24.

The transformer 9 is provided with a secondary winding 25 having connections A, B and C with a resistor 26 and a condenser 21. forming a phase-shift network 28 which supplies to the control grid 29 of the thyratron l5, through a transformer 30, an alternating voltage which lags the alternating voltage applied to the anode I8 of the tube, by a phase angle of the order of 99. The secondary winding 3| of the transformer 39 is connected to the control grid 29 through a suitable grid resistance 32, and to the cathode 26 through a grid condenser 33.

The secondary Winding 3| of transformer 3|] serves as a convenient means of superimposing on the alternating voltage, applied to the grid 29, a unidirectional grid biasing voltage in order to cause the output current of the thyration l5 to be increased or decreased in accordance with whether such unidirectional voltage is increased or decreased.

The transformer 9 supplies power to a potentiometer or voltage divider 34 through a full wave rectifier tube 35, the output circuit 36 of which includes a filter comprising a condenser 31 which acts to smooth the pulsating direct current output of the rectifier tube 35. The adjustable tap 38 of the voltage divider is connected to the control grid 29 by a circuit 39 which includes a 0" battery 40, secondary 8| oi transformer 30, and the resistor 32. The shunt field winding 4| of the motor 24 is also connected across the output circuit 35 of the rectifier 35.

Another potentiometer 42 is employed in the phase shift-network 28 to provide convenient .means for adjusting the amplitude of the phaseshift voltage.

It will be noted that this circuit is somewhat similar to that of Fig. 4 of application Serial No. 550,731, except for the addition of a starting resistor 43, a compensating circuit" 44 comprising resistors 45 and 46, and condenser 41. The starting resistor 43 and the resistor 45 are connected in series in the output circuit 22 of the thyratron 45 along with the armature winding 23 of the motor 24. The resistor 46 and the condenser 41 are connected in series with each other to ground at 48,

and in parallel with the resistor 45 which is connected to ground at 49. The negative terminal of the potentiometer 34 is connected by conductor 50 to the circuit between the condenser 41 and resistor 46.

In operation the motor armature current flows through the resistor 45 and develops a compensating voltage across this resistor having the positive polarity shown in the drawing. The resistor 45 and condenser 41, serve to filter fluctuations in the voltage across resistor 45. This filtered voltage appears across condenser 41. Such voltage is in series with the other voltages which appear on the control grid 29 of the thyratron l5 and, therefore, it tends to make the grid voltage of the thyratron l5 more positive by a value proportional to the increase in armature current.

As the load on the motor 24 is increased, the armature current increases and, therefore, the voltage across condenser 41 increases, and this in turn causes the grid voltage of the thyratron l5 to become more and more positive, and thus tends to cause the motor speed to increase with the motor load. With the proper value of resistor 45, any increase in motor load will develop a compensating voltage of exactly the right value necessary to compensate for any drop in speed due to change in load and thus the motor speed is made practically independent of load over a wide range.

As an example of the improvement which can be expected, tests on a motor with the unimproved generator governor control showed that a maximum speed range of approximately 100 to 1 could be obtained without exceedin percent regulation. With the compensating circuit 44 added, however, a speed range of better than 600 to 1 was obtained without exceeding 10 percent regu-' lation.

Furthermore, the regulation throughout the entire speed range was much better with the compensated circuit 44 than with the non-compensated circuit. For example, the regulation between 10 and 1000 revolutions per minute of the motor 24 was substantially zero percent for the compensated unit and ranged from 55 percent at 0 R. P. M. down to approximately V of 1 percent at 1000 R. P. M. for the non-compensated circuit. At 3 R. P. M. the regulation was 16.5 percent ior the compensated type and approximately 190 percent for the non-compensated type. At 1750 R. P. M. the regulation was /4 of 1 percent for the compensated type and 2.5 percent for the non-compensated type.

The above results were obtained with a fixed resistance value of resistor 45. When resistor 45 is adjustable so that the most suitable resistance 4 value for a given speed is chosen, the regulation of the motor 24 is practically zero throughout the entire speed range; Resistor and the speed adjusting potentiometer tap 38 are arranged so that they can be simultaneously adjusted by a common control 52.

If desired, the compensating circuit can be made to increase the speed of .the motor as the load is increased by properly selecting the resistance value of resistor 45.

Since the inciusion of the starting resistor 43 without any automatic shorting means tends to make the motor 24 slow down with an increase in load, and a property chosen value of resistor 45 in the compensated circuit 44 tends to make the motor speed increase with an increase in load, these circuits are combined with opposing efiects to get exceptionally good regulation. Thus, goodmotor performance is obtained without the additional parts and circuit complications normally required to short out the starting resistor. The starting resistor 43 remains in the armature circuit of the motor at all times, i. e.. when the motor is running as well as during the starting thereof.

The above description is concerned with a circuit in which the starting resistance is in series with the armature at all times. However, the compensating circuit 44 will also improve the regulation of this circuit when the starting resistance 43 is shorted out after the starting period or when a starting resistance is not used. The circuit described in application Serial No. 550,731 has good regulation over a wide range. By means of the compensatin circuit 44 the regulation is further improved and the useful speed range further extended. By the proper selection of the values of the components the speed-load regulation can be made substantially zero over a wide range.

One simple type of compensating circuit 44 is shown, but any compensating circuit which is connected in series with the motor armature to deliver to the grid of the control tube a positive voltage proportional to the armature current is within the scope of this invention. For example, it is possible to supply further filtering action by inserting another resistance and condenser such as 46 and 41 in connection 50 or to substitute an inductance for resistor 46.

I claim:

1. An electrical regulating system for governing the speed of a direct current shunt motor, comprising a thyratron type tube having an output circuit including the armature winding of said motor, a phase-shift network operatively associated with said tube, a resistor in said output circuit which tends to make the armature slow down with an increase in load during the running of the motor, and a compensating circuit consisting of a first resistor in series with said resistor, and a second resistor and a condenser in parallel with said first resistor, connected-to the control grid of the tube through a source of constant potential which is adjustable to adjust the speed of the motor, which compensating circuit tends to make the armature speed increase with an increase in load, so that the regulation of the speed of the motor is not adversely aiiected by the starting resistor during the running of the motor, the first resistor being adjustable so that the most suitable resistance value thereof for a given speed of the motor can be chosen, whereby the regulation of the motor is practically zero throughout the entire speed range, and common means for simultaneously adjusting both the effective voltage of the source of constant potential and the eiTective resistance of the first resistor.

2. An electrical regulating system for maintaining substantially constant the speed of a shunt wound motor, comprising the combination with an electronic speed control of the type in which a reference voltage that is adjustable to set the motor speed to the desired value, is matched by a voltage proportional to the speed of the motor and the difference between such voltages maintains such speed at a substantially constant value, of means for adding to such reference voltage a voltage that is proportional to the motor load comprising a thyratron, means for supplying an alternating voltage to the input circuit of said thyratron, means for passing the output of said thyratron through the armature of said motor, a resistor connected in series with said armature, and means connected across said resistor to carry over from one cycle into the next cycle a voltage proportional to the current through said resistor.

3. An electrical regulating system for maintaining substantially constant the speed of 'a motor. comprising in combination a thyratron, means for supplying an alternating voltage to the input of said thyratron, means for passing the rectified current output of the thyratron through the armature of the motor, means for selecting the speed at which the motor will operate including means for applying to the grid of the thyratron a unidirectional negative voltage proportional to the speed of the motor, an alternating voltage lagging the plate voltage by approximately 90", a unidirectional positive voltage proportional to the desired motor speed, and a unidirectional positive voltage proportional to the motor load.

4. An electrical regulating system for maintaining substantially constant the speed of a shunt wound motor, comprising the combination of a thyratron, means for supplying an alternating voltage to the input of said thyratron, a resistor connected in series with the armature of the motor, means for passing the output of the thyratron through the armature of the motor and said resistor connected in series with such armature, means connected across said resistor to carry over from one cycle into the next cycle a voltage proportional to the current through the resistor, such proportional voltage being added to a negative voltage proportional to the speed of the motor, a positive voltage proportional to the desired motor speed. and an alternating voltage lagging the input voltage of the thyratron by approximately 90, the algebraic sum of such voltages being applied to the grid of the thyratron to control its output so as to maintain the desired motor speed.

5. An electrical regulating system for maintaining substantially constant the speed of shuntwound motor comprising the combination of a thyratron, means for supplying an alternating voltage to the input circuit of said thyratron, means for passing the output of said thyratron through the armature of said motor, a resistor connected in series with said armature, means connected across said resistor to carry over from one cycle into the next cycle, a voltage proportional to the current through said resistor, means for obtaining a negative voltage proportional to the motor armature counter E. M. F. voltage, means for obtaining a positive voltage proportional to a desired motor speed, means for'obtaining an alternating voltage lagging the input voltage of the thyratron by approximately and means for applying the algebraic sum of such voltages to the grid of said thyratron to maintain the desired motor speed.

6. An electrical regulating system for governing the speed of a direct current shunt motor, comprising a thyratron type tube having an output circuit including the armature winding of said motor, a phase-shift network operatively associated with said tube, a resistor in said output circuit and a compensating circuit consisting of a first resistor in series with said resistor, and a second resistor and a condenser in parallel with said first resistor, connected to the control grid of the tube through a source of constant potential which is adjustable to adjust the speed of the motor, which compensating circuit tends to make the armature speed increase with an increase in load, said first resistor being adjustable so that the most suitable resistance value thereof for a given speed of the motor can be chosen, whereby the regulation of the motor is practically zero throughout the entire speed range, and common means for simultaneously adjusting both the efiective voltage of the source of constant potential and the effective resistance of the first resistor.

ROSCOE R. LOBOSCO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,847,934 Elder et al. Mar. 1, 1932 1,985,003 Von Engel et al. Dec. -18, 1934 2,082,496 Howe June 1, 1937 2,445,789 Lobosco July 27, 1948 

